1. Field of the Invention
The present invention relates to photosensitive hardenable compositions which are hardened upon exposure to light and developable with alkaline aqueous solutions. More particularly, the present invention relates to photopolymerizable hardenable compositions showing improved properties in softness, stripping properties, stripping time, etc. of hardened layers formed.
2. Description of the Related Art
In general, photopolymerizable hardenable compositions are laminated in base plates (for example, a copper-clad laminate), metal surfaces suitable for minute finishing, etc., by conventional coating or lamination methods. Upon exposure to actinic light, exposed areas are hardened and unexposed areas are dissolved and removed with solvents having a suitable solubility. The solvents are roughly classified into organic solvents such as 1,1,1-trichloroethane and aqueous solvents such as sodium carbonate aqueous solution.
In recent years, photopolymerizable hardenable compositions which are developed using aqueous solvents have been increasingly used in view of operational environments, natural environments and production costs.
However, photopolymerizable hardenable compositions of aqueous solvent development type involve many restrictions in etching or a plating treatment as compared to the case of using conventional photopolymerizable hardenable compositions of organic solvent development type and, often cause problems upon use.
Particularly in the case of using alkaline treating solutions, acidic thermoplastic high molecular binders are fundamentally used so that the use is greatly restricted.
In addition, hardened layers after pattern formation through etching or plating are rigid and fragile and thus often scraped off base plates, as compared to the case of using conventional photopolymerizable hardenable compositions of organic solvent development type. Further, a long period of time is required for stripping hardened layers. Furthermore, stripped layers do not go into pieces but become so called "seaweed"-like so that a problem of causing readhesion and difficulties in reproduction by filtration of stripping solutions become serious problems in operations.
The present inventors have previously proposed a photopolymerizable hardenable composition comprising specific thermoplastic high molecular binders as described below wherein trimethylolpropane triacrylate as an addition polymerizable compound is used in combination with a photopolymerizable initiator (Published Unexamined Japanese patent application No. 153308/87). However, this photopolymerizable hardenable composition has defects that a stripping time is long and hardened layers lack softness. Therefore, the present inventors have made further investigations and as a result, found that by incorporating specific addition polymerizable compounds therein, excellent photopolymerizable hardenable compositions can be obtained.